EP1630914B1 - Vertically emitting semiconductor laser with external resonator and its method of fabrication - Google Patents
Vertically emitting semiconductor laser with external resonator and its method of fabrication Download PDFInfo
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- EP1630914B1 EP1630914B1 EP20050016990 EP05016990A EP1630914B1 EP 1630914 B1 EP1630914 B1 EP 1630914B1 EP 20050016990 EP20050016990 EP 20050016990 EP 05016990 A EP05016990 A EP 05016990A EP 1630914 B1 EP1630914 B1 EP 1630914B1
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- 239000004065 semiconductor Substances 0.000 title claims description 53
- 238000004519 manufacturing process Methods 0.000 title claims description 11
- 238000005253 cladding Methods 0.000 claims description 22
- 239000002019 doping agent Substances 0.000 claims description 21
- 230000000903 blocking effect Effects 0.000 claims description 19
- 230000005855 radiation Effects 0.000 claims description 14
- 238000000034 method Methods 0.000 claims description 6
- 239000000758 substrate Substances 0.000 claims description 6
- 238000009792 diffusion process Methods 0.000 claims description 3
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical group [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 2
- 229910052725 zinc Inorganic materials 0.000 claims description 2
- 239000011701 zinc Substances 0.000 claims description 2
- 230000005540 biological transmission Effects 0.000 claims 8
- 230000000694 effects Effects 0.000 claims 1
- 229910000980 Aluminium gallium arsenide Inorganic materials 0.000 description 4
- 229910001218 Gallium arsenide Inorganic materials 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 230000002411 adverse Effects 0.000 description 2
- 230000004888 barrier function Effects 0.000 description 2
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- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 238000013139 quantization Methods 0.000 description 2
- 229910000530 Gallium indium arsenide Inorganic materials 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 239000002800 charge carrier Substances 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/14—External cavity lasers
- H01S5/141—External cavity lasers using a wavelength selective device, e.g. a grating or etalon
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
- H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
- H01S5/18308—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a special structure for lateral current or light confinement
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
- H01S5/2054—Methods of obtaining the confinement
- H01S5/2059—Methods of obtaining the confinement by means of particular conductivity zones, e.g. obtained by particle bombardment or diffusion
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/305—Structure or shape of the active region; Materials used for the active region characterised by the doping materials used in the laser structure
- H01S5/3054—Structure or shape of the active region; Materials used for the active region characterised by the doping materials used in the laser structure p-doping
Definitions
- the present invention relates to a vertically emitting semiconductor laser according to the preamble of claim 1 and a method for its production.
- a generic radiation-emitting semiconductor laser is for example from the document WO 02/13334 A2 known.
- a vertically emitting laser in the form of a so-called VCSEL (Vertical Cavity Surface Emitting Laser).
- This VCSEL has a semiconductor body with a laser resonator formed by two resonator mirrors, wherein in the laser resonator inter alia an active layer and a current constriction layer are arranged.
- the Stromeinschnürungstik used in operation to concentrate the operating current to a small portion of the active layer to generate there required for laser operation population inversion.
- Such surface emitting VCSELs are characterized by a high beam quality, but have a comparatively low optical output power.
- the electrical heat loss Beam quality or stability could adversely affect.
- VECSELs Very External Cavity Surface Emitting Lasers
- Such semiconductor lasers with an external resonator usually have a much larger lateral extent than a VCSEL and are operated at correspondingly higher powers.
- the diameter of a VECSEL is in the range of 10 ⁇ m or even more. Due to the widely differing lateral dimensioning, the concepts for guiding the operating current in a VCSEL are generally not transferable to a VECSEL.
- An external-cavity vertically-emitting semiconductor laser comprises a radiation-emitting semiconductor body having a vertical emission direction, comprising a current-guiding layer disposed within the semiconductor body having a current blocking region and a current transmitting region, and a radiation-generating active layer, the external resonator having a predetermined resonator volume overlapping with the current-passing region ,
- the operating current is led to a region in the semiconductor body which is suitable for generating radiation within the resonator volume.
- a coupling of the operating current is made possible via an electrical contact arranged outside the resonator volume, so that on the one hand this contact does not hinder the radiation extraction and on the other hand, an advantageous current flow is ensured for an efficient laser operation.
- a radiation exit side is provided in the semiconductor body and a predetermined radiation exit region is provided on the radiation exit side, an electrical contact for impressing the operating current being arranged in the semiconductor body outside this radiation exit region.
- the current blocking region of the current-carrying layer is arranged downstream of the electrical contact in the vertical direction, so that a current flow outside the resonator volume of the external resonator, which does not or only inefficiently contributes to the generation of radiation, is avoided.
- the current blocking region is formed by means of at least one pn junction blocking during operation.
- Such blocking pn junctions can be produced with relatively little technical effort.
- the current-carrying layer is arranged between two cladding layers of a first conductivity type and has a second conductivity type in the current-blocking region.
- the current-carrying layer in the current blocking region in conjunction with the adjacent cladding layers in each case forms a pn junction, wherein the forward directions of these pn junctions are opposite to one another and thus prevent current flow through the current blocking region.
- the current-carrying layer has the first one Line type, so that in this area no blocking pn junctions are arranged.
- the current-carrying layer is doped in the current-carrying region with dopants of the first and the second conductivity type. This facilitates the production of a corresponding semiconductor body, since first the current-carrying layer can be doped continuously with dopants of the second conductivity type. Subsequently, the current-carrying layer is selectively doped in the current-conducting region with a dopant of the first conductivity type in such a way that the doping of the first conductivity type predominates and the conductivity type is reversed so that overall the current-conducting region has the first conductivity type.
- a mirror structure for forming the external resonator is furthermore arranged in the semiconductor body.
- the mirror structure may be formed, for example, as a Bragg mirror. This facilitates the construction of the external resonator, since in addition to the semiconductor body only an external mirror is required.
- the external resonator mirror is preferably a concave mirror, by which the laser radiation is more preferably coupled out.
- a suitable dimensioning of the radius of curvature to the resonator length such a resonator has an advantageously increased stability compared to a Fabry-Perot resonator with planar resonator mirrors.
- the semiconductor body is formed by an epitaxial process, successively growing a first cladding layer of a first conductivity type, the second conductivity type current-conducting layer, and a second cladding layer of the first conductivity type, and subsequently the current-guiding layer within the current passage region is doped with a dopant such that the current passage region has the first conductivity type.
- a dopant source with the corresponding dopant is preferably applied in a structured manner to the second cladding layer in a region downstream of the current passage region in the vertical direction and subsequently the dopant diffuses into the current passage region. After the diffusion process, the dopant source can be removed again.
- a semiconductor body 1 seen in the vertical direction comprises a substrate 2, a mirror layer 3, an active layer 4, a first cladding layer 5, a current-carrying layer 6 and a second cladding layer 7.
- a first electrical contact 9 preferably in the form of a ring contact, is formed.
- a continuous electrical contact 10 is arranged on the opposite side of the semiconductor body.
- the laser resonator is formed by the mirror layer 3 and an external mirror 11, preferably with a curved mirror surface.
- the mirror layer 3 can be embodied in a manner known per se as a Bragg mirror having a plurality of alternating semiconductor layers with different refractive indices.
- As a material system for such layers for example, GaAs / AlGaAs is suitable, wherein the layer sequence is composed of layer pairs 3a, 3b with different aluminum content.
- a metal mirror or a dielectric mirror may be provided, in which case the substrate 2 may be expediently eliminated.
- this mirror can also be used as a contact 10.
- the current-carrying layer 6 is arranged between two cladding layers 5 and 7 of a first conductivity type and also has the first conductivity type in the current-carrying region 13.
- the current-carrying layer 6 has a second conductivity type, so that seen in the vertical direction together with the adjacent cladding layers 5 and 7, two pn junctions with opposite forward direction are formed which prevent a vertical current flow in the current blocking region 12.
- an n-doped GaAs substrate may be provided as the substrate 2, onto which an n-doped GaAs / AlGaAs Bragg mirror is grown.
- the active layer 4 is preferably designed as a single or multiple quantum well structure (SQW - single quantum well or MQW - multiple quantum well).
- Such quantum well structures usually have one (SQW) or several (MQW) quantum well layers, which are arranged between barrier layers.
- the quantum well structures may contain InGaP, InGaAs or GaAs quantum well layers and / or AlInGaP or AlGaAs barrier layers, respectively.
- spacer layers can be provided between the individual quantum wells.
- quantum well structure encompasses any structure in which charge carriers undergo quantization of their energy states by confinement.
- Name Quantum well structure No information about the dimensionality of the quantization. It thus includes quantum wells, quantum wires and quantum dots and any combination of these structures.
- the active layer 4 for example, a p-type InGaP layer embedded between two AlGaInP layers is suitable.
- a p-doped first cladding layer 5 a current-carrying layer 6 n-doped in the current blocking regions 12 and p-doped in the current-carrying region 13, and a p-doped second cladding layer 7.
- These three semiconductor layers 5, 6 and 7 can For example, AlGaAs or AlGaInP included. In this way, a blocking npn junction, that is to say a series connection of two opposite pn junctions, is formed in the current blocking regions 12.
- the lateral width of the current passage region 13 is selected in the invention such that the current passage region overlaps with the predetermined resonator volume 14 of the external resonator, wherein the current passage region is preferably wider than the lateral cross section of the resonator volume 14 in the region of the current-carrying layer 6 shown embodiment, in particular by the resonator length in conjunction with the radius of curvature of the external mirror 11 set.
- the 1 / e 2 radius of the basic electromagnetic field in the Gaussian approximation can be used as resonator limit in the present invention.
- FIG. 1 In the Figures 2a, 2b and 2c is based on three intermediate steps, an inventive manufacturing method for in FIG. 1 shown semiconductor body shown.
- a mirror structure 3 having a sequence of layer pairs 3a, 3b with a different refractive index, an active layer 4, a first cladding layer 5, a current-carrying layer 6 and a second cladding layer 7 is first epitaxially grown on a substrate 2.
- the first cladding layer 5 continuously has a first conductivity type
- the current-carrying layer 6 has a second conductivity type continuously
- the second cladding layer 7 has the first conductivity type.
- the first cladding layer 5 may be p-doped
- the current-carrying layer 6 may be n-doped
- the second cladding layer 7 may again be p-doped.
- the current blocking region 12 and the current passage region 13 of the current-carrying layer 6 are formed.
- a dopant source 15 is applied in a structured manner to the second cladding layer 7, in a region downstream of which the current passage region 13 is arranged in the vertical direction.
- the dopant source 15 contains a dopant of the first conductivity type, which is subsequently diffused into the underlying layers and in particular into the current-carrying layer 6.
- the doping is carried out in such a way that in the current passage region 13 of the current-carrying layer 6, the conductivity type is reversed. In this way, a vertical current path of the first conductivity type is formed in the current passage region.
- a dopant for the above-mentioned semiconductor materials for example, zinc is suitable.
- an electrical contact 9, for example a ring contact, and on the opposite side of the semiconductor body a continuous electrical contact 10 corresponding thereto are subsequently formed on the radiation-decoupling side 8 of the semiconductor body.
- the ring contact is in this case arranged so that the ring opening is arranged downstream of the current passage region 13 in the vertical direction. In this way, it is ensured that the contact 9 does not engage in the intended resonator volume and adversely affects the radiation extraction from the semiconductor body.
- the present invention is not limited to said semiconductor materials, such that the layers of the semiconductor body also include another material such as In x Al y Ga 1-xy As where 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1 and 0 ⁇ x + y ⁇ 1, In x Al y Ga 1-xy P with 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1 and 0 ⁇ x + y ⁇ 1, In x Al y Ga 1-xy N with 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1 and 0 ⁇ x + y ⁇ 1, In x Al y Ga 1-xy As u N 1-u with 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1, 0 ⁇ x + y ⁇ 1 and 0 ⁇ u ⁇ 1, In x Al y Ga 1-xy As u P 1-u with 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1, 0 ⁇ x + y ⁇ 1 and 0 ⁇ u ⁇ 1, and / or In x Al y Ga 1-xy As where 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1 and 0 ⁇ x + y
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- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Optics & Photonics (AREA)
- Semiconductor Lasers (AREA)
Description
Die vorliegende Erfindung bezieht sich auf einen vertikal emittierenden Halbleiterlaser nach dem Oberbegriff des Patentanspruchs 1 sowie ein Verfahren zu dessen Herstellung.The present invention relates to a vertically emitting semiconductor laser according to the preamble of claim 1 and a method for its production.
Ein gattungsgemäßer strahlungsemittierender Halbleiterlaser ist beispielsweise aus der Druckschrift
Derartige oberflächenemittierende VCSEL zeichnen durch eine hohe Strahlqualität aus, besitzen aber eine vergleichsweise geringe optische Ausgangsleistung. Zudem ist, wie in der oben genannten Druckschrift beschrieben, auf eine wohldefinierte Stromführung zu achten, da ansonsten aufgrund der Nähe von Strompfad und Laserresonatorvolumen in Verbindung mit den vergleichsweise geringen lateralen Ausdehnungen eines solchen Halbleiterlasers die elektrische Verlustwärme die Strahlqualität beziehungsweise die Stabilität negativ beeinflussen könnte.Such surface emitting VCSELs are characterized by a high beam quality, but have a comparatively low optical output power. In addition, as described in the cited document, to pay attention to a well-defined current flow, otherwise due to the proximity of current path and laser resonator volume in conjunction with the comparatively small lateral dimensions of such a semiconductor laser, the electrical heat loss Beam quality or stability could adversely affect.
In der Druckschrift
Ferner beschreibt die Druckschrift
Weiterhin ist bekannt, zur Steigerung der optischen Ausgangsleistung statt eines in den Halbleiterkörper integrierten Laserresonators einen Resonator mit einem externen Resonatorspiegel vorzusehen. Derartige Vorrichtungen werden auch als VECSEL (Vertical External Cavity Surface Emitting Laser) bezeichnet. Solche Halbleiterlaser mit einem externen Resonator weisen üblicherweise eine sehr viel größere laterale Ausdehnung als ein VCSEL auf und werden mit entsprechend höheren Leistungen betrieben. So liegt typischerweise der Durchmesser eines VECSELs im Bereich von 10 µm oder sogar darüber. Aufgrund der stark unterschiedlichen lateralen Dimensionierung sind in der Regel die Konzepte zur Führung des Betriebsstroms bei einen VCSEL nicht auf einen VECSEL übertragbar.It is furthermore known to provide a resonator with an external resonator mirror instead of a laser resonator integrated in the semiconductor body in order to increase the optical output power. Such devices are also referred to as VECSELs (Vertical External Cavity Surface Emitting Lasers). Such semiconductor lasers with an external resonator usually have a much larger lateral extent than a VCSEL and are operated at correspondingly higher powers. Typically, the diameter of a VECSEL is in the range of 10 μm or even more. Due to the widely differing lateral dimensioning, the concepts for guiding the operating current in a VCSEL are generally not transferable to a VECSEL.
Es ist Aufgabe der vorliegenden Erfindung, einen vertikal emittierenden Halbeiterlaser mit einem Halbleiterkörper mit hoher Ausgangsleistung und einer verbesserten Stromführung zu schaffen. Ferner soll der Halbleiterkörper des vertikal emittierenden Halbleiterlasers mit geringem technischem Aufwand herstellbar sein. Weiterhin ist es Aufgabe der vorliegenden Erfindung, ein Herstellungsverfahren für einen erfindungsgemäßen vertikal emittierenden Halbliterlaser anzugeben.It is an object of the present invention to provide a vertically emitting semiconductor laser with a semiconductor body having a high output power and an improved current conduction. Furthermore, the semiconductor body of the vertically emitting semiconductor laser should be producible with little technical effort. It is a further object of the present invention to specify a production method for a vertically emitting semiconductor laser according to the invention.
Diese Aufgabe wird durch einen vertikal emittierenden Halbleiterlaser gemäß Patentanspruch 1 sowie ein Herstellungsverfahren gemäß Patentanspruch 8 gelöst. Vorteilhafte Weiterbildungen der Erfindung sind Gegenstand der abhängigen Ansprüche.This object is achieved by a vertically emitting semiconductor laser according to claim 1 and a manufacturing method according to
Ein erfindungsgemäßer vertikal emittierender Halbleiterlaser mit externem Resonator umfasst einen strahlungsemittierenden Halbleiterkörper mit vertikaler Emissionsrichtung, der eine innerhalb des Halbleiterkörpers angeordnete Stromführungsschicht mit einem Stromsperrbereich und einem Stromdurchlassbereich sowie eine strahlungserzeugende aktive Schicht aufweist, wobei der externe Resonator ein vorgegebenes Resonatorvolumen aufweist, das mit dem Stromdurchlassbereich überlappt.An external-cavity vertically-emitting semiconductor laser according to the present invention comprises a radiation-emitting semiconductor body having a vertical emission direction, comprising a current-guiding layer disposed within the semiconductor body having a current blocking region and a current transmitting region, and a radiation-generating active layer, the external resonator having a predetermined resonator volume overlapping with the current-passing region ,
Durch die Anpassung der Stromführungsschicht an das durch den externen Resonator vorgegebene Resonatorvolumen wird der Betriebsstrom zu einem für die Strahlungserzeugung innerhalb des Resonatorvolumens zweckmäßigen Bereich in dem Halbleiterkörper hingeführt. Hierdurch wird eine Einkopplung des Betriebsstroms über einen außerhalb des Resonatorvolumens angeordneten elektrischen Kontakt ermöglicht, so dass einerseits dieser Kontakt die Strahlungsauskopplung nicht behindert und andererseits eine vorteilhafte Stromführung für einen effizienten Laserbetrieb gewährleistet ist.By adapting the current-carrying layer to the resonator volume predetermined by the external resonator, the operating current is led to a region in the semiconductor body which is suitable for generating radiation within the resonator volume. As a result, a coupling of the operating current is made possible via an electrical contact arranged outside the resonator volume, so that on the one hand this contact does not hinder the radiation extraction and on the other hand, an advantageous current flow is ensured for an efficient laser operation.
Entsprechend ist bei einer bevorzugten Ausführungsform der vorliegenden Erfindung bei dem Halbleiterkörper eine Strahlungsaustrittsseite und auf der Strahlungsaustrittsseite ein vorgegebener Strahlungsaustrittsbereich vorgesehen, wobei außerhalb dieses Strahlungsaustrittsbereichs ein elektrischer Kontakt zur Einprägung des Betriebsstroms in den Halbleiterkörper angeordnet ist. Bevorzugt ist der Stromsperrbereich der Stromführungsschicht dem elektrischen Kontakt in vertikaler Richtung nachgeordnet, so dass ein Stromfluss außerhalb des Resonatorvolumens des externen Resonators, der zur Strahlungserzeugung nicht oder nur in ineffizienter Weise beiträgt, vermieden wird.Accordingly, in a preferred embodiment of the present invention, a radiation exit side is provided in the semiconductor body and a predetermined radiation exit region is provided on the radiation exit side, an electrical contact for impressing the operating current being arranged in the semiconductor body outside this radiation exit region. Preferably, the current blocking region of the current-carrying layer is arranged downstream of the electrical contact in the vertical direction, so that a current flow outside the resonator volume of the external resonator, which does not or only inefficiently contributes to the generation of radiation, is avoided.
Der Stromsperrbereich ist bei einer vorteilhaften Weiterbildung der vorliegenden Erfindung mittels mindestens eines im Betrieb sperrenden pn-Übergangs gebildet. Derartige sperrende pn-Übergänge können mit vergleichsweise geringem technischen Aufwand hergestellt werden.In an advantageous development of the present invention, the current blocking region is formed by means of at least one pn junction blocking during operation. Such blocking pn junctions can be produced with relatively little technical effort.
Die Stromführungsschicht ist zwischen zwei Mantelschichten eines ersten Leitungstyps angeordnet und weist in dem Stromsperrbereich einen zweiten Leitungstyp auf. Bei dieser Anordnung bildet die Stromführungsschicht in dem Stromsperrbereich in Verbindung mit den benachbarten Mantelschichten jeweils einen pn-Übergang, wobei die Durchlassrichtungen dieser pn-Übergänge einander entgegengesetzt sind und somit einen Stromfluss durch den Stromsperrbereich verhindern. In dem Stromdurchlassbereich weist hingegen die Stromführungsschicht den ersten Leitungstyp auf, so dass in diesem Bereich keine sperrenden pn-Übergänge angeordnet sind.The current-carrying layer is arranged between two cladding layers of a first conductivity type and has a second conductivity type in the current-blocking region. In this arrangement, the current-carrying layer in the current blocking region in conjunction with the adjacent cladding layers in each case forms a pn junction, wherein the forward directions of these pn junctions are opposite to one another and thus prevent current flow through the current blocking region. In the current passage region, by contrast, the current-carrying layer has the first one Line type, so that in this area no blocking pn junctions are arranged.
Die Stromführungsschicht ist in dem Stromdurchlassbereich mit Dotierstoffen des ersten und des zweiten Leitungstyps dotiert. Dies erleichtert die Herstellung eines entsprechenden Halbleiterkörpers, da zunächst die Stromführungsschicht durchgehend mit Dotierstoffen des zweiten Leitungstyps dotiert werden kann. Nachfolgend wird gezielt in dem Stromdurchlassbereich die Stromführungsschicht mit einem Dotierstoff des ersten Leitungstyps derart dotiert, dass die Dotierung des ersten Leitungstyps überwiegt und der Leitungstyp umgekehrt wird, so dass insgesamt der Stromdurchlassbereich den ersten Leitungstyp aufweist.The current-carrying layer is doped in the current-carrying region with dopants of the first and the second conductivity type. This facilitates the production of a corresponding semiconductor body, since first the current-carrying layer can be doped continuously with dopants of the second conductivity type. Subsequently, the current-carrying layer is selectively doped in the current-conducting region with a dopant of the first conductivity type in such a way that the doping of the first conductivity type predominates and the conductivity type is reversed so that overall the current-conducting region has the first conductivity type.
Bei einer vorteilhaften Ausgestaltung der vorliegenden Erfindung ist in dem Halbleiterkörper weiterhin eine Spiegelstruktur zur Bildung des externen Resonators angeordnet. Die Spiegelstruktur kann beispielsweise als Bragg-Spiegel ausgebildet sein. Dies erleichtert den Aufbau des externen Resonators, da zusätzlich zu dem Halbleiterkörper nur noch ein externer Spiegel erforderlich ist.In an advantageous embodiment of the present invention, a mirror structure for forming the external resonator is furthermore arranged in the semiconductor body. The mirror structure may be formed, for example, as a Bragg mirror. This facilitates the construction of the external resonator, since in addition to the semiconductor body only an external mirror is required.
Vorzugsweise ist der externe Resonatorspiegel ein konkav gekrümmter Spiegel, durch den weiter bevorzugt die Laserstrahlung ausgekoppelt wird. Bei geeigneter Dimensionierung des Krümmungsradius zur Resonatorlänge weist ein derartiger Resonator gegenüber einem Fabry-Perot-Resonator mit planen Resonatorspiegeln eine vorteilhaft erhöhte Stabilität auf.The external resonator mirror is preferably a concave mirror, by which the laser radiation is more preferably coupled out. With a suitable dimensioning of the radius of curvature to the resonator length, such a resonator has an advantageously increased stability compared to a Fabry-Perot resonator with planar resonator mirrors.
Zur Herstellung eines erfindungsgemäßen vertikal emittierenden Halbleiterlasers wird bei der vorliegenden Erfindung der Halbleiterkörper mittels eines Epitaxieverfahrens gefertigt, wobei nacheinander eine erste Mantelschicht eines ersten Leitungstyps, die Stromführungsschicht eines zweiten Leitungstyps und eine zweite Mantelschicht des ersten Leitungstyps aufgewachsen wird, und nachfolgend die Stromführungsschicht innerhalb des Stromdurchlassbereichs mit einem Dotierstoff derart dotiert wird, dass der Stromdurchlassbereich den ersten Leitungstyp aufweist.In the present invention, in order to fabricate a vertical emission type semiconductor laser according to the present invention, the semiconductor body is formed by an epitaxial process, successively growing a first cladding layer of a first conductivity type, the second conductivity type current-conducting layer, and a second cladding layer of the first conductivity type, and subsequently the current-guiding layer within the current passage region is doped with a dopant such that the current passage region has the first conductivity type.
Ein derartiges Herstellungsverfahren erfordert einen vergleichsweise geringen technischen Aufwand, da zusätzlich zum epitaktischen Aufwachsen der Halbleiterschichten nur eine strukturierte Diffusion innerhalb der Stromdurchlassbereichs erforderlich ist.Such a production method requires comparatively little technical effort since, in addition to the epitaxial growth of the semiconductor layers, only structured diffusion within the current passage region is required.
Bevorzugt wird zur Dotierung des Stromdurchlassbereichs eine Dotierstoffquelle mit dem entsprechenden Dotierstoff strukturiert auf die zweite Mantelschicht in einem Bereich aufgebracht, dem der Stromdurchlassbereich in vertikaler Richtung nachgeordnet ist und nachfolgend der Dotierstoff in den Stromdurchlassbereich diffundiert. Nach dem Diffusionsprozess kann die Dotierstoffquelle wieder entfernt werden.For doping the current passage region, a dopant source with the corresponding dopant is preferably applied in a structured manner to the second cladding layer in a region downstream of the current passage region in the vertical direction and subsequently the dopant diffuses into the current passage region. After the diffusion process, the dopant source can be removed again.
Weitere Merkmale, Vorzüge und Zweckmäßigkeiten der Erfindung ergeben sich aus der nachfolgenden Beschreibung von zwei Ausführungsbeispielen in Verbindung mit den
Es zeigen:
-
Figur 1 eine schematische Schnittansicht eines Ausführungsbeispiels eines Halbleiterkörpers eines erfindungsgemäßen Halbleiterlasers und -
eine schematische Darstellung eines Ausführungsbeispiels eines erfindungsgemäßen Herstellungsverfahrens anhand von drei Zwischenschritten.Figur 2
-
FIG. 1 a schematic sectional view of an embodiment of a semiconductor body of a semiconductor laser according to the invention and -
FIG. 2 a schematic representation of an embodiment of a manufacturing method according to the invention with reference to three intermediate steps.
Gleiche oder gleichwirkende Elemente sind in den Figuren mit den selben Bezugszeichen versehen.The same or equivalent elements are provided in the figures with the same reference numerals.
Das in
Der Laserresonator wird von der Spiegelschicht 3 und einem externen Spiegel 11, bevorzugt mit gekrümmter Spiegelfläche, gebildet. Die Spiegelschicht 3 kann in an sich bekannter Weise als Bragg-Spiegel mit einer Mehrzahl alternierender Halbleiterschichten mit unterschiedlichem Brechungsindex ausgeführt sein. Als Materialsystem für derartige Schichten eignet sich beispielsweise GaAs/AlGaAs, wobei die Schichtfolge sich aus Schichtpaaren 3a, 3b mit unterschiedlichem Aluminiumgehalt zusammensetzt. Alternativ kann als Spiegelstruktur 3 auch ein Metallspiegel oder ein dielektrischer Spiegel vorgesehen sein, wobei in diesem Fall das Substrat 2 zweckmäßigerweise entfallen kann. Weitergehend kann im Fall eines Metallspiegels dieser Spiegel zugleich als Kontakt 10 verwendet werden.The laser resonator is formed by the mirror layer 3 and an
Die Stromführungsschicht 6 ist zwischen zwei Mantelschichten 5 und 7 eines ersten Leitungstyps angeordnet und weist in dem Stromdurchlassbereich 13 ebenfalls den ersten Leitungstyp auf. In den Stromsperrbereichen 12 hingegen weist die Stromführungsschicht 6 einen zweiten Leitungstyp auf, so dass in vertikaler Richtung gesehen zusammen mit den angrenzenden Mantelschichten 5 und 7 zwei pn-Übergänge mit entgegengesetzter Durchlassrichtung gebildet sind, die einen vertikalen Stromfluss im Stromsperrbereich 12 verhindern.The current-carrying layer 6 is arranged between two
Beispielsweise kann als Substrat 2 ein n-dotiertes GaAs-Substrat vorgesehen sein, auf das ein n-dotierter GaAs/AlGaAs Bragg-Spiegel aufgewachsen ist.For example, an n-doped GaAs substrate may be provided as the
Die aktive Schicht 4 ist bevorzugt als Einfach- oder Mehrfachquantentopstruktur (SQW - single quantum well bzw. MQW - multiple quantum well)ausgeführt. Derartige Quantentopfstrukturen weisen in der Regel eine (SQW) bzw. mehrere (MQW) Quantentopfschichten auf, die zwischen Barriereschichten angeordnet sind. Beispielsweise können die Quantentopfstrukturen InGaP-, InGaAs- oder GaAs-Quantentopfschichten und/oder AlInGaP- beziehungsweisew AlGaAs-Barriereschichten enthalten. Weiterhin können zwischen den einzelnen Quantentöpfen Spacerschichten vorgesehen sein.The
Die Bezeichnung Quantentopfstruktur umfasst im Rahmen der Anmeldung jegliche Struktur, bei der Ladungsträger durch Einschluss ("confinement") eine Quantisierung ihrer Energiezustände erfahren. Insbesondere beinhaltet die Bezeichnung Quantentopfstruktur keine Angabe über die Dimensionalität der Quantisierung. Sie umfasst somit u.a. Quantentröge, Quantendrähte und Quantenpunkte und jede Kombination dieser Strukturen.Within the scope of the application, the term quantum well structure encompasses any structure in which charge carriers undergo quantization of their energy states by confinement. In particular, the Name Quantum well structure No information about the dimensionality of the quantization. It thus includes quantum wells, quantum wires and quantum dots and any combination of these structures.
Ferner eignet sich als aktive Schicht 4 beispielsweise eine p-dotierte InGaP-Schicht, die zwischen zwei AlGaInP-Schichten eingebettet ist.Further, as the
Hierauf folgt in vertikaler Richtung gesehen eine p-dotierte erste Mantelschicht 5, eine in den Stromsperrbereichen 12 n-dotierte und in dem Stromdurchlassbereich 13 p-dotierte Stromführungsschicht 6 und eine p-dotierte zweite Mantelschicht 7. Diese drei Halbleiterschichten 5, 6 und 7 können beispielsweise AlGaAs oder AlGaInP enthalten. Damit wird in den Stromsperrbereichen 12 ein sperrender npn-Übergang, also eine Serienschaltung zweier entgegengesetzter pn-Übergänge, gebildet.This is followed in the vertical direction by a p-doped
Die laterale Breite des Stromdurchlassbereichs 13 ist bei der Erfindung so gewählt, dass der Stromdurchlassbereich mit dem vorgegeben Resonatorvolumen 14 des externen Resonators überlappt, wobei bevorzugt der Stromdurchlassbereich breiter ist als der laterale Querschnitt des Resonatorvolumens 14 im Bereich der Stromführungsschicht 6. Das Resonatorvolumen wird bei dem gezeigten Ausführungsbeispiel insbesondere durch die Resonatorlänge in Verbindung mit dem Krümmungsradius des externen Spiegels 11 festgelegt. Im Zweifel kann als Resonatorbegrenzung bei der vorliegenden Erfindung der 1/e2-Radius des elektromagnetischen Grundmodenfeldes in Gausscher Näherung herangezogen werden.The lateral width of the
In den
In einem ersten Schritt,
In einem zweiten Schritt,
In einem dritten Schritt,
Die Erläuterung der Erfindung anhand der Ausführungsbeispiele ist nicht als Beschränkung der Erfindung hierauf zu verstehen. Insbesondere ist die vorliegende Erfindung nicht auf die genannten Halbleitermaterialien beschränkt, so dass die Schichten des Halbleiterkörpers auch ein anderes Material wie etwa InxAlyGa1-x-yAs mit 0≤x≤1, 0≤y≤1 und 0≤x+y≤1,
InxAlyGa1-x-yP mit 0≤x≤1, 0≤y≤1 und 0≤x+y≤1,
InxAlyGa1-x-yN mit 0≤x≤1, 0≤y≤1 und 0≤x+y≤1,
InxAlyGa1-x-yAsuN1-u mit 0≤x≤1, 0≤y≤1, 0≤x+y≤1 und 0≤u≤1,
InxAlyGa1-x-yAsuP1-u mit 0≤x≤1, 0≤y≤1, 0≤x+y≤1 und 0≤u≤1, und/oder
InxAlyGa1-x-yPuN1-u mit 0≤x≤1, 0≤y≤1, 0≤x+y≤1 und 0≤u≤1 enthalten können.The explanation of the invention with reference to the embodiments is not to be understood as limiting the invention thereto. In particular, the present invention is not limited to said semiconductor materials, such that the layers of the semiconductor body also include another material such as In x Al y Ga 1-xy As where 0≤x≤1, 0≤y≤1 and 0≤x + y ≦ 1,
In x Al y Ga 1-xy P with 0≤x≤1, 0≤y≤1 and 0≤x + y≤1,
In x Al y Ga 1-xy N with 0≤x≤1, 0≤y≤1 and 0≤x + y≤1,
In x Al y Ga 1-xy As u N 1-u with 0≤x≤1, 0≤y≤1, 0≤x + y≤1 and 0≤u≤1,
In x Al y Ga 1-xy As u P 1-u with 0≤x≤1, 0≤y≤1, 0≤x + y≤1 and 0≤u≤1, and / or
In x Al y Ga 1-xy P u N 1-u with 0≤x≤1, 0≤y≤1, 0≤x + y≤1 and 0≤u≤1.
Claims (11)
- Vertically emitting semiconductor laser with an external resonator,
having a radiation-emitting semiconductor body (1) with a vertical emission direction, comprising a radiation-generating active layer (4) and a current-carrying layer (6) with a current blocking region (12) and a current transmission region (13), wherein- the current-carrying layer (6) is arranged between two cladding layers (5, 7) of a first conduction type and has a second conduction type in the current blocking region (12),- the current-carrying layer (6) has the first conduction type in the current transmission region (13) and- the external resonator has a predetermined resonator volume (14) that overlaps the current transmission region (13),characterized in that
the current-carrying layer (6) is doped with dopants of the first and of the second conduction type in the current transmission region (13). - Vertically emitting semiconductor laser (1) according to Claim 1,
characterized in that
the semiconductor body (1) has a radiation exit side (8) and a radiation exit region that is predetermined on the radiation exit side (8), wherein an electrical contact (9) is arranged outside the radiation exit region. - Vertically emitting semiconductor laser (1) according to Claim 2,
characterized in that
the current blocking region (12) is disposed downstream of the electrical contact (9) in a vertical direction. - Vertically emitting semiconductor laser (1) according to one of Claims 1 to 3,
characterized in that
the current blocking region (12) is formed by means of at least one pn junction that effects blocking during operation. - Vertically emitting semiconductor laser (1) according to one of Claims 1 to 4,
characterized in that
a mirror structure (3) for forming the external resonator is formed in the semiconductor body (1). - Vertically emitting semiconductor laser (1) according to Claim 5,
characterized in that
the mirror structure (3) is a Bragg mirror. - Vertically emitting semiconductor laser (1) according to one of Claims 1 to 6,
characterized in that
the external resonator has a curved external mirror (11). - Method for fabricating a vertically emitting semiconductor laser according to one of Claims 1 to 7, comprising the steps of- providing a growth substrate,- epitaxially growing the active layer (4), and- forming the current-carrying layer,characterized in that
the current-carrying layer is formed by the steps of:- growing a first cladding layer (5) of a first conduction type,- growing the current-carrying layer (6) of a second conduction type,- growing a second cladding layer (7) of the first conduction type, and- doping the current-carrying layer (6) within the current transmission region (13) with a dopant in such a way that the current transmission region (13) has the first conduction type. - Fabrication method according to Claim 8,
characterized in that
for the doping of the current-carrying layer (6), a dopant source (15) with the dopant is applied to the second cladding layer (7) in patterned fashion in a region downstream of which the current transmission region (13) is disposed in a vertical direction, and the dopant subsequently diffuses into the current transmission region (13). - Fabrication method according to Claim 9,
characterized in that
the dopant source (15) is removed after the diffusion of the dopant. - Fabrication method according to Claim 9 or 10,
characterized in that
the dopant is zinc.
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US6862301B2 (en) * | 2001-12-31 | 2005-03-01 | Finisar Corporation | Tunable laser assembly |
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